1. Field of the Invention
The present invention relates to electrically conductive silicone elastomer compositions, methods for manufacturing semiconductor devices, and semiconductor devices. More specifically, the present invention relates to electrically conductive silicone elastomer compositions which are curable to form silicone elastomers having outstanding electrical conductivity. When the electrically conductive silicone elastomer composition is applied to a substrate and the periphery of the the composition is cured, the composition will not containminate the substrate, nor the environment in the proximity of the substate, with low-molecular-weight silicone species prior to complete cure of the composition via a hydrosilylation reaction. The present invention also more specifcally relates to methods of manufacturing semiconductor devices using the electrically conductive silicone elastomer compositions of the present invention whereby the electriclaly conductive silicone elatomer composition is used to adhere a semiconductor chip to a substrate, whereby the wire bondability of the semiconductor device is not adversely affected and adhesion defects between the semiconductor chip, substrate, package, or lead frame and the sealing resin can be minimized. The present invention also relates to semiconductor devices manufactured by this method which have outstanding reliability.
Electrically conductive silicone elastomer compositions which are curable to silicone elastomers are used, for example, as adhesives for adhereing quartz oscillators to crystal resonators, crystal components of crystal filters, etc., and for adhereing piezoelectric substrates on packages, as shielding agents for electromagnetic wave shielding, and as die bonding agents for adhering semiconductor chips to substrates, packages, etc.
When conventional electrically conductive silicone elastomer compositions are use to bond semiconductor chips to substrates, packages, etc., there are problems with wire bondability (i.e., bonding properties of the bonding wire) to the semiconductor chip or lead frame and with defects in adhesion of the semiconductor chip, substrate, package, or lead frame and the sealing resin, which- causes a deterioration in the moisture resistance of the semiconductor device.
2. Description of the Related Art
In order to solve these problems, an electrically conductive silicone elastomer composition has been proposed in which the amount of volatile low-molecular-weight siloxane is reduced and curing is carried out by means of a hydrosilylation reaction (See Japanese Unexamined Patent Application No. H3-170581), but even in the case of this electrically conductive silicone elastomer composition, the decrease in wire bondability to the semiconductor chip or lead frame and the adhesion defects between the semiconductor chip, substrate, package, or lead frame and the sealing resin were not sufficiently inhibited, and the moisture resistance of the semiconductor device could not be sufficiently improved.
By means of various studies, it was confirmed that when an electrically conductive silicone elastomer composition curable by means of a hydrosilylation reaction is used to adhere a semiconductor chip to a substrate, low-molecular-weight silicone species outgas from the electrically conductive silicone elastomer. composition prior to and/or during cure of the composition via a hydrosilylation reaction. The low-molecular-weight species contaminate the surface of the semiconductor chip, substrate, package, lead frame, etc., and cause a decrease in wire bondability to the semiconductor chip or lead frame and adhesion defects between the semiconductor chip, substrate, packages or lead frame and the sealing resin. The low-molecular-weight silicone species were determined to be cyclic siloxane contained in the organopolysiloxane which is the main component of electrically conductive silicone elastomer compositions, an organopolysiloxane for curing electrically conductive silicone elastomer compositions, or an organopolysiloxane for improving the adhesion of electrically conductive silicone elastomer compositions.
For this reason, the inventors of the present invention prepared an electrically conductive silicone elastomer composition, cured the composition at room temperature via a hydrosilylation reaction, and attempted to inhibit outgassing of low-molecular-weight silicone oil from the electrically conductive silicone elastomer composition before and during curing. The handling and workability of such an electrically conductive silicone elastomer composition were extremely poor.
Moreover, the inventors of the present invention attempted to prevent outgassing by mixing an electrically conductive filler with an acrylic functional group-containing silicone elastomer composition which was curable via a free radical reaction induced by high-energy beam irradiation. The acrylic functional group-containg silicone elastomer composition, however, did not sufficiently cure because the high-energy beam was unable to sufficiently penetrate to the inner portion of the silicone elastomer composition because of the presence of the the electrically conductive filler. The portion of the composition into which the high energy beam did not penetrate did not cure.
The present inventors conducted thorough studies on the above problems and discovered that the compositions of the present invention exhibit decreased outgassing of low-molecular-weight silicone species. Such outgassing is minimized by the use of an acrylic functional group-containing organopolysiloxane that participates in a free radical reaction when induced by a high-energy beam and by the use, in the present composition, of siloxane components which are curable via a hydrosilyation reaction.
The composition of the present invention can be used to adhere a semiconductor chip to a substrate. If the chip-composition-substrate composite is irradiatied with high energy radiation, the exposed surfaces of the composition will cure. Once the exposed surfaces are cured, the problem of low-molecular weight silicone species contamination is minimized or eliminated. The composition is then allowed to cure via a hydrosilyation reaction to form a silicone elastomer having outstanding electrical conductivity.
The present inventors also discovered that after a semiconductor chip is mounted on a substrate or package using the composition of the present invention, and the chip-composition-substrate composite is irradiated with high-energy radiation, a free radical reaction involving the acrylic functional group-containing organopolysiloxane occurs on the surfaces of the composition which are exposed to such high-energy radiation. As a result, outgassing of low-molecular-weight silicone species from the composition is sufficently inhibited such that the composition may be allowed to fully cure via a hydrosilylation reaction.
Specifically, the purpose of the present invention is to provide an electrically conductive silicone elastomer composition which forms a silicone elastomer having outstanding electrical conductivity in which the periphery of the electrically conductive silicone elastomer composition may be cured via irradiation with a high energy beam such that contamination by low-molecular-weight silicone oil before or during cured is averted; a method for manufacturing a semiconductor device in which, during adhesion of a semiconductor chip to the substrate, package, etc., by means of this composition, decreases in wire bondability to the semiconductor chip or lead frame and adhesion defects between the semiconductor chip, substrate, package, or lead frame and the sealing resin can be inhibited; and a semiconductor device manufactured by this method which has outstanding moisture resistance.